The present invention is related to the field of network communications.
In the field of network communications, there is often a distinction made between communications features and mechanisms that operate at a physical layer as opposed to those having a more “logical” or functional characteristic. An example of physical-layer features of a communications network include the physical cables between network elements or devices, along with the hardware interfaces to such cables within the network devices. Some network cables may be designed for use with optical communications signals, whereas other cables may be designed for use with non-optical electrical signals. An example of the latter type of cable includes standard “unshielded twisted pair” or UTP cables such as commonly employed in telephone and data communications systems. There is widespread use of so-called “Category 5” cable which includes multiple (e.g. 4) unshielded twisted pairs, each capable of data signaling rates on the order of 100 Mb/s.
The term “Ethernet” refers to a family of specifications for a widely used physical data communications technique that commonly employs a multi-twisted-pair cable such as Category 5 cable. According to respective specifications for 10BaseT and 100BaseT Ethernet, a point-to-point Ethernet link includes one twisted pair used for data transmission in one direction and a second twisted pair for data transmission in the other direction. Thus in each case a single twisted pair is used to carry the entire data communications signal from one end to the other. According to a more recent specification for 1000BaseT (also referred to as “gigabit Ethernet” or “GbE”), data transmission occurs in a more complex manner. A 1-Gb/s data signal is de-multiplexed into four 250-Mb/s signals, and each of these is transmitted over a corresponding one of 4 twisted pairs using a multi-level encoding scheme. Also, a duplex technique is employed such that transmission occurs in both directions simultaneously. That is, the signal appearing on any given twisted pair actually represents an electrical sum of a 250-Mb/s signal traveling in one direction and an independent 250-Mb/s signal traveling in the other direction. To receive data, a device at either end of the cable uses a technique referred to as “echo cancellation” to subtract its own transmission from the signal it receives from the cable, and thereby recover the signal that was transmitted by the far-end device.
Ethernet also employs a technique referred to as “auto-negotiation” by which two end devices on a point-to-point link engage in an initial dialogue to establish the speed at which the link is to operated along with other parameters such as whether half-duplex or full-duplex communications will be used. Generally, auto-negotiation is biased toward the communications mode that will deliver the highest performance. Thus if both ends of a link are capable of operating at 1000BaseT, for example, then such operation will be established automatically even though both ends might also be capable of lower-speed operation. In auto-negotiation, lower-speed operation will only be chosen if operation at higher speeds is not possible.
It has been known to use various security techniques within communications networks to provide protection from damage and/or unauthorized use. At the very highest levels, there can be passwords and similar mechanisms employed for authenticating users of applications and/or network resources. More at the level of network communications per se, it has been known to use data encryption techniques by which the payloads of data “packets” are made to be unintelligible to anybody who might intercept them and who is not privy to the encryption keys. Such techniques have been deployed at the more logical or functional layers of network operation, such as within applications programs, operating systems, and network communications drivers. Although they are also deployed at the physical layer, the circuitry for implementing them is very specialized and often expensive in terms of the area it requires on an integrated circuit.